1. Field of the Invention
The present invention relates to a communication apparatus used to communicate movement-related information between mobile units such as vehicles.
2. Description of Related Art
For instance, one such conventional apparatus used for sending and receiving signals between mobile units such as vehicles is described in Patent Document 1. With this apparatus, when a vehicle detects information regarding traffic flow and emergencies, etc., the vehicle can transmit the information to all vehicles within range of possible wireless transmission.
However, high-frequency signals are normally used for wireless communication in car-to-car communication systems. Consequently, the problem is that when there are communication obstacles, such as, for instance, buildings, etc., that shield high-frequency signals, communication with cars in their shadow is rendered impossible.
On the other hand, a well-known mobile communication technology, called multi-hop wireless network technology, permits communication between mobile units that cannot communicate with one another directly by relaying signals via a plurality of mobile units. In addition, routing protocols have been developed for building routes in various multi-hop wireless networks. In other words, communication between mobile units and a mobile unit to which signals cannot be sent directly is made possible by relaying signals via other mobile units (e.g., see Patent Document 2).
Patent Document 1: JP 2001-283381A (paragraph 0077 through Paragraph 0079, see FIG. 9).
Patent Document 2: JP 2001-237764A (pages 3 through 7, see FIG. 1, FIG. 4, and FIG. 6).
However, due to the fact that hopping in multi-hop wireless networks of mobile units happens in a disorderly fashion, the problem is that route convergence requires more time, which degrades communication efficiency.